One solution to the problem of sensorineural (inner ear) deafness is to bypass the damaged hair cells of the inner ear and directly stimulate the remaining auditory nerve fibers electrically. The effectiveness of producing auditory sensations in this manner is well documented in several hundred implanted patients but very few have had any measureable useful speech discrimination. Various coding approaches have been attempted and those using mutichannel scala tympani stimulation with electrode position representing place pitch have been the most promising. The basic principle of the more promising approaches is to attempt to produce auditory nerve response patterns in frequency specific auditory nerve sub-populations that mimic the response patterns of a similar sub-population of neurons to acoustic stimulation through a normal cochlea. Little is known about the effects of the design parameters of the scala tympani implants on VIII nerve single neuron responses. This project is designed to fill this void and determine the following: (1) the effect of physical implant electrode parameters (service area, radial spacing between pairs), (2) the effects of stimulating electrode configuration (bipolar radial, bipolar longitudinal, monopolar, and pseudobipolar with distributed return), (3) the effect of the electrical stimulating patterns (sine wave, square wave, pulse rate, pulse width and stimulus frequency), (4) the effects of (2) and (3) on electrical stimulus interaction from two channels stimulated simultaneously with in-phase or out-of-phase signals, (5) how to avoid unwanted stimulus interaction and how to use stimulus interaction to an advantage. Documenting the responses to implant stimulation at the auditory nerve single neuron level and determining how to best manipulate these responses for normal physiology similarity will be a significant step in interpreting present clinical results with cochlear prostheses, in understanding the coding of the auditory neurophysiologic process, and in developing a cochlear prosthesis coding scheme that will produce valuable speech discrimination to the implanted deaf patient, our overall goal.